The show really lost something when Larry David called it quits after season 7, never was that more evident than in the show's final run.
There was a malaise over the actors during that season that just wasn't there before, and that tiredness permeated the whole show. Upon a re-watch, season 9 just isn't up at the level that the others were.
That being said season 9 had its good moments. Looking at episodes such as 'The Merv Griffin Show,' in which Kramer finds the set of the old Merv Griffin Show and sets it up in his apartment. As well as 'The Junk Mail', in which Kramer tries to stop his mail from being delivered completely.
It was clear that the show had come to its natural end, with Jerry Seinfeld rejecting a huge payday of over $100 million for a tenth season.
All this mixed with the polarising reception to the final episode 'The Finale' meant that Seinfeld was ready to go without a fuss from all who worked on it.